Photographic developer containing hindered phenols



3,186,843 PHOTOGRAPHIC DEVELOPER CONTAINING HINDERED PHENOLS Howard C. Haas, Arlington, Mass, assignor to Polaroid Corporation, Cambridge, Mass, a corporation of Delaware No Drawing. Filed Apr. 27, 1962, Ser. No. 190,792

. 6 Claims. (Cl. 96-66) This invention relates to photography and, more particularly, to photographic developers of improved and advantageous characteristics.

One object of this invention is to provide a novel photographic developing agent for exposed silver halide.

Another object or" this invention is to provide a novel photographic developing agent that will develop exposed silver halide on an equimolar basis.

Another object is to provide a non-aqueous developing system for developing exposed silver halide.

Still another object is to provide 'a novel silver halide developing agent that does not form colored condensation products.

Still another object is to provide novel processes for developing exposed silver halide emulsions wherein the silver halide developing agent is a hindered phenol.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description.

The Theory of the Photographic Process, C. E. K., Mees, Second Edition, 1954, Macmillan Company, New York, N.Y., at page 577, reports traces of development with certain hindered phenols. However, unusually extreme conditions are described as necessary to produce even the reported traces of development. For these reasons, such phenols were not of any practical interest and have only been studied from a scientific viewpoint.

It has now been found that certain hindered phenols will develop exposed silver halide compounds. The abovereported unusually extreme conditions are not necessary; the novel silver halide developing agents of this invention readily reduce exposed silver halide. Up to ten times faster development than the hindered phenol developing agent of the cited reference has been noted with the novel compounds of this invention.

The novel silver halide developing agents of this invention may be utilized in aqueous developing systems or in substantially non-aqueous systems. When a non-aqueous system is employed, the developing composition preferably contains a solvent for the particular silver halide emulsion colloid binder to provide the necessary swelling of the emulsion to speed development. For example, with a hydroxyethyl-polyvinyl alcohol silver halide emulsion a solvent comprising methanol may be used and a solvent comprising dimethyl sulfoxide may be used with a gelatin ice emulsion. A gelatin emulsion or hydroxyethyl-polyvinyl alcohol emulsion may also be used with an aqueous silver halide developing composition.

Hydroxyethyl-polyvinyl alcohol silver halide emulsions suitable for use in this invention are disclosed and claimed in the copending US. application of W. H. Ryan, Serial No. 170,008, filed January 31, 1962. Gelatin silver halide emulsions suitable for use in this invention are known to the art.

The novel silver halide developing agents of this invention are hindered phenols wherein the a-hydrogens on the carbon atoms on the ring ortho to the hydroxyl radical have been replaced by alkyl radicals in which the carbon attached to the ring is fully substituted. In a preferred embodiment, the novel silver halide developing agents of this invention may be represented by the formula:

CH CH 11-6 at is, in.

wherein R is a methyl or ethyl group, X is a lower alkyl or a solubilizing group, such as a carboxy-alkoxy or carboxy-alkylene radical, to provide solubility of the compound in an aqueous alkaline solution. The term alkyl is intended to include radicals such as methyl, ethyl, tertbutyl and tert-amyl.

In an aqueous developing composition, the silver halide developing agent wherein X is a solubilizing group is preferably used, to permit solubilization of the compound in an aqueous alkaline solution. In developing compositions utilizing a compound of Formula 1, wherein X is an alkyl radical, only a very small amount of water may be present due to the insolubility characteristics of the phenols; preferably, an entirely non-aqueous system is used.

By utilizing non-aqueous developing systems containing suitable organic solvents to swell the particular silver halide emulsion, development can proceed at a satisfactory rate.

A non-aqueous developing composition within this invention comprises the hindered phenol developing agent, e.g., 2,4,6-tri-tert-butyl phenol, a solvent for the hindered phenol, e.g., methanol, a solvent as a swelling agent for the particular emulsion, and alkali, e.g., sodium hydroxide. Preferably, the solvent for the developing agent and the solvent for swelling the emulsion are the same.

An aqueous developing composition within this invention comprises the hindered phenol developing agent of Formula 1 wherein X is a solubilizing group, e.g., 3,5-t'

buty1-4-hydroxy-phenoxy acetic acid, a solvent forthe hindered phenol, alkali, and water.

Other materials, such as thickeners, restrainers, accel: erators, etc., may also be added to the developing com position as desired.

The hindered phenol developers of this invention may also be added to silver halide developing compositions, particularly in color processes, as auxiliary developers.

As examples of hindered phenol silver halide develop- G ing agents within the scope of this invention, mention may be made of the following:

( 1) 2,4,6-tri-tert-butyl phenol (2) 2,6-di-tert-butyl-4-methyl phenol OH (3H3 CH3 CH -O (J-CH3 (EH3 1 (EH3 I CH COOH The following nonlimiting examples illustrate the aqueous silver halide developing compositions within the scope of this invent-ion:

Example 3 2,6,di-tert-butyl-4-carboxymethoxy phenol percent 5 Sodium hydroxide do 4 Hydroxyethylcellulose do 4 Water cc 100.0

The hindered phenols of Formula 1 wherein X is an alkyl radical are known to the art and may be prepared by known methods.

' 2,6,-di-tert-butyl-4-carboxymethoxy phenol may be. prepared in the following manner;

Example 4' To 20 gm. of 2,4,6-tri-tert-butyl phenol dissolved in 250 ml. of benzene was added a solution of 75 gm. of potassium ferricyanide and 25 gm. of potassium hyroxide in 250 ml. of water. The reaction mixture was stirred and oxygen was bubbled through the mixture for 3 hours. The yellow benzene layer was separated and washed with hexadiene-4-one was recrystallized from ethanol and showed a melting point of 140 C. gm. of the 1,3,5- t-ri-tert-butyl 2,5cyclohcxadiene-4one were cracked at 207 C. The mixture was dissolved in 7 ml. of cyclohexane and 7 ml; of glacial acetic acid. Five drops of water were added and a small amount of zinc dust. The mixture was heated to reflux until the dark brown color had become yellow. The resulting 2,6-di-tert-butyl hydroquinone was extracted under nitrogen with 2% sodium hydroxide and isolated by neutralization with concentrated hydrochloric acid. 2 gm. of this product, melting at 101-102 C., was added to 30 ml. of methanol con taining 2 gm. of sodium hydroxide under nitrogen. 1.8 gm. of chloroaceticacid in 10 ml. of methanol was added and the mixture was heated at reflux with stirring for 2 hours. The pH of the solution was then adjusted to 3 with dilute hydrochloric acid; The resultingsolid was then dissolved in ether and extracted with several wash ings with saturated sodium bicarbonate solution. The bicarbonate solution was neutralized with concentrated hydrochloric acid to yield a white solid. The solid, 2,6- di-tert-butyl-4-carboxymethoxy phenol, was washed with water and purified by recrystallization from ligroinmethanol and showed a melting point of 163-164' C.

The hindered phenols of Formula 1 wherein X is a carboxy-alkylene radical may be prepared, for example, by reacting 2,6-di-tert-butyl phenol with succinic'anhydride to give:

CH CH5 Gila-(i l CH CH CH and reducing the group by a Clemmensen reduction reaction to the methylene group.

The silver halide devoloping compositions of Examples 1 through 4 were used in the following manner: A photosensitive silver halide emulsion was exposed to a stepwedge image.- In the dark, the exposed emulsion was brought into superposed relationship with a transparent sheet of cellulose acetate as the developing composition was spread therebetween. Silver development was observed by infrared light through the cellulose acetate sheet. When the developing composition of Example 3 was tested in this manner with a gelatino silver. halide emulsion, appreciable silver density was observed after 10 seconds.

Since certain changes may be made in the above products and processes without departing from the scope of the invention herein involved, .it is intended that all matter contained in the above description shall be interpreted as illustrative and not in .a limiting sense.

What is claimed is;

1. A process of developing an exposed silver halide OH 3. l 3

R- G-R in, on,

I wherein R-is a lower alkyl radical and X is selected from water, dried over magnesium sulfateand then evaporated to dryness. The resulting 1,3,5-tri-tert-butyl-2,S-cyclothe groupconsisting of tertiary butyl, tertiary amyl, methyl, carboxy-alkoxy and carboxy-alkylene radicals.

2. A process as defined in claim 1 wherein X is a methyl radical. V

3. A process as defined in claim 1 wherein X is a tertbutyl radical.

4. A process as defined in claim 3 wherein said solution is a methanol solution.

5. A process of developing an exposed silver halide emulsion which comprises treating said emulsion with a substantially non-aqueous alkaline solution comprising 2,4,6-tri-tert-butyl phenol.

6. A process of developing an exposed silver halide emulsion which comprises treating said emulsion with a substantially non-aqueous alkaline solution comprising 2,6-di-tert-butyl 4-methyl phenol.

References Cited by the Examiner UNITED STATES PATENTS 7/62 De Ratnaix et al 969 OTHER REFERENCES Becconsall et al.: Proceedings Chemical Society, pp. 308-9 (1959).

Fairb'ourn et al.: Proceedings Chemical Society, pp. 67-8 (1960).

Mees: The Theory of the Photographic Process, pp. 549 and 577, Revised Edition. The Macmillan Company, New York (1954).

NORMAN G. TORCHIN, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,186,843 June 1, 1965 Howard C. Haas Column 3, lines 24 to 31, for that portion of the formula reading I read T C CH2=COOH H -COOH column 4, lines 29 to 58, for that portion of the formula reading CH CH 4 3 I 3 CH read CHE-C- CH CH same column 4, line 44, for "developing" read developing Signed and sealed this 7th day of December 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A PROCESS OF DEVELOPING AN EXPOSED SILVER HALIDE EMULSION WHICH COMPRISES TREATING SAID EMULSION WITH A SUBSTANTIALLY NON-AQUEOUS ALKALINE SOLUTION COMPRISING A HINDERED PHENOL OF THE FORMULA: 